Well completion system

ABSTRACT

A well completion system comprises production tubing (5) extending downhole from wellhead equipment (2) to a plurality of completion systems (7, 8, 9). A well testing facility comprising a test loop (26) with flow metering equipement (27) is included in the wellhead equipment. Each of a plurality of independently adjustable flow control means (57) is operable to stop the flow of fluid from a respective one of the completion assemblies into the production tubing. The downhole completion assemblies (7, 8, 9) are mounted on a common fluid and electrical supply means (4) comprising tubular electrical conductor means (42) and tubing (41, 45, 46) defining fluid paths.

The invention relates to a well completion system and is concerned withthe provision of such a system incorporating features providing enhancedproduction from the well.

The invention accordingly provides a well completion system comprisingat least one downhole completion assembly for receiving fluid from areservoir, selectively adjustable flow control means in the completionassembly, and a fluid flow booster downstream of the completionassembly, whereby the fluid extraction rate can be optimised.

The system can include a plurality of completion assemblies in series,each incorporating a respective flow control means, typically a chokedevice, for individual adjustment of fluid inflow from respectivereservoirs associated with the completion assemblies or from a singlereservoir at spaced intervals at which the assemblies are located. Theextracted fluid can comprise liquid or gas or a mixture of the two, anda submersible pump or a compressor is selected as the flow or productionbooster accordingly.

The production booster functions to expose the reservoir or reservoirsto a higher drawdown pressure differential than is available from thenatural reservoir drive, thereby providing artificial lift. A singleproduction booster can be operated in conjunction with a plurality ofcompletion assemblies which can be individually tuned to a drawdownappropriate to the respective associated reservoirs or reservoirintervals, the adjustments being within a pressure range correspondingto the differential provided by the booster.

The invention thus also provides a completion assembly for a wellcompletion system comprising tubing for receiving well effluent and forguiding the received well effluent through a variable choke device,together with control means for varying the choke device flow aperture.The choke device is preferably operable to close off the effluent flowcompletely.

Such a completion assembly can be employed in various forms of wellcompletion system and the control means can be operated in response tosensed local conditions or in the context of overall system managementin a system incorporating plural completion assemblies.

The invention also provides a well completion system comprising aplurality of completion assemblies each having a selectively variablechoke device, wellhead equipment including a well testing facility, andcontrol means for operating the choke devices so as to permit testing atthe wellhead of individual wells, or of individual production intervalsof a single well.

The wellhead equipment can thus include a test loop with meteringfacilities. Where the system comprises plural wells tied back to commonflowlines, individual wells can be tested without interruption toproduction from other wells. The system can but need not include aproduction booster downstream of the completion assemblies, so as toprovide for optimised production as described above.

The invention also provides a well completion system comprising aplurality of downhole equipment units on a common core or spineconstituted by electrical and/or fluid supply means. The supply meanscan be constructed as power tubing extending centrally along theproduction tubing of the system.

The power tubing preferably includes plural conductors for thetransmission of electric power and also control signals downhole fromthe wellhead. The conductors also transmit test and monitoring signalsfrom the downhole equipment up to data acquisition and treatmentequipment at the wellhead. Multiplexing can be employed. The powertubing also preferably incorporates fluid passage means extendingbetween the wellhead and the downhole equipment. Plural conduits can beprovided for conveying or circulating for example barrier fluid forproviding overpressure protection, hydraulic fluid for operation ofdownhole equipment, as by way of local power units, and for the supplyof chemical additives or inhibitors to be injected into the productionfluid. Each unit of the downhole equipment accordingly has itsrespective electrical and/or fluid connections to the power tubing.

The invention also provides a well completion system comprisingmonitoring means at the wellhead, plural well completion assemblies, andvariable flow control device responsive to signals from the monitoringunit at each completion assembly, sensor means at each completionassembly supplying signals to the monitoring means to permit continuousinteractive control of production.

Such tuning of the system requires information about the performance of,and the conditions at, the (or each) completion assembly. The inventiontherefore also provides a well completion system includinginstrumentation associated with downhole equipment, means communicatingthe instrumentation with control equipment located at the wellhead, topermit monitoring and control of the system.

The sensor means can include sensors for logging reservoir andproduction flow parameters such as temperature, pressure, composition,and flow rates. Where the downhole equipment includes spaced completionassemblies receiving fluid from respective reservoirs or from respectivelocations in a single reservoir, the sensors can be arranged to logparameters of the respective fluid flows at the respective assemblies aswell as of the combined or commingled flow downstream of the assembliesand/or at the wellhead. Where a booster pump or compressor is provideddownstream of the (or each) completion assembly, this also canincorporate appropriate sensors at least for metering the flow and itscharacteristics. Data provided by the downhole sensor means is conveyed,conveniently, by way of the power tubing described above, if employed,to the monitoring unit at which the data is received, stored and treatedto provide information for automatic or manual control functions to beexercised from the wellhead on the various units of the downholeequipment. To optimise performance of the system in dependence on sensedvariations in reservoir characteristics. The downhole equipment can becontrolled as a whole or selectively in respect of its various units.

Where fluid is being extracted from a plurality of reservoirs, theconditions of each can be sensed independently, by way of theinstrumentation included in the associated completion assembly. Bycontinuous or selective monitoring of the well characteristics and theperformance of the downhole equipment, optimum control can be achievedby remote control without disturbing the functioning of the system andwithout the need to perform intervention operations.

A well completion system according to the invention can include forexample heaters spaced along it to maintain temperature control of thewell effluent for example to prevent deposition and solidification ofparticles, which might restrict the production flow. The or eachcompletion assembly can include a heater for aiding production of heavyoils, and means for injection of chemicals and additives to function asinhibitors to prevent scaling or dehydration can be provided, forexample, at the or each completion assembly. One or more downhole steamgenerators can be included for cyclic stimulation and subsequentextraction for example of heavy oils.

A well completion system incorporating the invention will be understoodto be very advantageously employed in subsea wells and horizontal wellsas well as subterrain wells, particularly in complex reservoirsituations and in reservoirs with thin pay zones.

The invention is further described below, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a well completion system in accordancewith the invention;

FIG. 2 is a schematic sectional side view on a larger scale of adownhole completion assembly included in the system of FIG. 1;

FIGS. 3 & 4 are cross-sectional views on lines III--III and IV--IV ofFIG. 2 respectively; and

FIG. 5 is a cross-sectional view on line V--V of FIG. 1.

The illustrated well completion system comprises, as shown in FIG. 1,wellhead equipment 2 including a completion and production tree fromwhich power tubing 4 extends downwardly within production tubing 5 to aproduction booster 6 and then to downhole completion equipmentconstituted here by three completion assemblies 7,8,9 spaced along thepower tubing and connected in series to it. The system is shown inoperative condition within a well bore containing a production casing 11extending down from the wellhead to a production casing shoe 12.

The production tubing 5 extends down to the booster 6 which is locatedjust below the production casing shoe 12. Beyond the booster, aproduction liner 14 extends through three reservoirs 15,16 & 17.

The wellhead production tree is designed to accommodate all systemrequirements. Thus besides structural integrity, the production treeprovides for the supply of electric power from a source 21, and fluids,such as hydraulic and barrier fluids and chemical additives, fromsources 22, along the power tubing 4. The tree is also arranged tofacilitate retrieval and workover. Also included in the wellheadequipment 2 is an electronic data handling and control unit 24 at whichis collected data from sensors located downhole and from which aretransmitted command signals for controlling operation of the downholeequipment. The data and command signals are multiplexed for transmissionalong power conductors of the power tubing and are taken from andsupplied to these conductors at 25.

The equipment 2 also provides a production test loop 26 with meteringequipment 27 which can be employed to test separate remote wells tiedback to common flowlines by way of subsea manifold installations. Eachwell may be tested individually without interrupting the production fromother wells. Because of the nature of the downhole equipment, eachreservoir or reservoir interval may be tested individually withoutintervention operations.

The power tubing 4 is preferably of concentric configuration and asshown in FIG. 5 can comprise outer protective tubing 41 having receivedwithin it with spacing to provide a first fluid conduit 44 a tubularconductor assembly. The conductor assembly consists of three concentrictubular electrical conductors 42, electrically insulated by interveningsleeves of dielectric material. Inner and outer concentric spaced tubes45 & 46 are received within the conductor assembly to provide threefurther fluid conduits 47.

The power tubing can comprise sections of appropriate length, typically9-15 meters, connected together by appropriate joint means 49 indicatedschematically in FIG. 5. The power tubing equipment is run into the wellbore by conventional techniques during installation, and provides forcontinuous distribution of electrical and fluid supplies through theentire system, as well as for conveyance of test, measurement andcontrol signals between the wellhead control unit 24 and the variousunits downhole.

Referring now to the three downhole completion assemblies 7, 8 & 9,these are employed because the drainhole section of the well borepenetrates the three separate reservoirs 15, 16 & 17, but pluralassemblies could be employed where a long drainhole section in a singlereservoir is divided into individual production locations. Each of thecompletion assemblies 7, 8 & 9 controls the well inflow from theassociated reservoir which it supplies into a mixed or commingled flowwhich is moved into the production tubing 5 by way of the booster 6.

FIGS. 2-4 show the uppermost completion assembly 7 of FIG. 1 receivedwithin the production liner 14 which has perforations or slots along itover the length of the assembly to permit fluid communication betweenthe assembly and the reservoir. The production liner 14 is sealed to thebore by packers 51 (or conventionally by cementing) which serve toseparate the slotted or perforated liner sections communicating with onereservoir from those communicating with another.

The completion assembly 7 has been set in position, after installation,by inflatable completion seals 52 which serve to isolate the inflow fromthe downstream reservoirs 16 & 17. The assembly comprises tubing 54concentrically surrounding the power tubing 4 to provide therewith anannular conduit for the mixed or commingled flow from the upstreamassemblies through apertured upper and lower annular end walls 55,56. Atthe downstream end of the assembly, between the tubing 54 and the upperseal 52, a production choke 57 is provided to control the productionflow from the adjacent reservoir. The flow through the choke 57 mixeswith the flow through the end wall 55 in the space between theproduction liner 14 and the power tubing 4 and moves upwardly to thedownhole production booster 6.

The production choke 57 provides a fixed annular series of flowapertures 58, the effective area of which can be selectively adjusted byrotation of a similarly apertured annulus between a fully open position,in which the fixed apertures coincide with those of the annulus, and afully closed position, as shown in FIG. 4, in which the fixed aperturescoincide with the solid portions of the annulus between its apertures.The production choke 57 is thus adjustable to control the quantity ofthe well effluent flowing into the commingled flow upstream of theassembly 7. The choke 57 can be employed to tune the completion assemblyproduction and is drawn down to provide optimum reservoir extractioncharacteristics and to control the pressure of the common productionflow.

The choke 57 is controlled from the wellhead equipment by signals fromthe control unit 24 carried by the power tubing 4 and is actuated by alocal hydraulic power pack 59 supplied by the hydraulic supplies withinthe power tubing.

Besides the power pack 59, the assembly 7 includes instrumentation 60with sensors for logging and monitoring operation of the assembly. Thesensor outputs are supplied to the wellhead control unit 24 by means ofthe power tubing 4 through a data acquisition and transmission unit 61.Means 62 for injection into the production flow of an inhibitor or otherchemical additive from the source 22 can be provided, as can a heater 64for local production stimulation.

A downhole steam generator 65, which can be operated to enhanceproduction particularly of heavy oils, is provided downstream of thecompletion assemblies, and one or more production flow heaters 66(FIG. 1) can be located at spaced positions between the booster 6 andthe wellhead to maintain optimum production temperatures and preventwaxing, scaling etc. The additional downhole equipment described iscontrolled and powered from the wellhead by way of the power tubing 4.

Each of the completion assemblies 8 & 9 is similar in function andconfiguration to the assembly 7 and neither is therefore furtherdescribed. Between adjacent assemblies, an annular chamber 70 betweenthe production liner 14 and the power tubing 4 serves as a mixingchamber for the flow from the adjacent assembly and the assembly orassemblies upstream. As for the production booster 6, a downholesubmersible pump may be employed where the production fluid is a liquidor primarily a liquid, but the booster can be constituted by acompressor where the completion system is applied to a gas producingreservoir or reservoirs.

The booster 6 serves as a common booster for all three of the completionassemblies 7, 8 & 9. It adds an additional drawn down capacity to thenatural flow conditions which is selected in accordance with thecalculations based on tests of the reservoir inflow performance. Theproduction booster 6 and chokes 57 of the completion assemblies thus areoperated to tune the extraction process and provide optimum productionrates of the commingled production flow through the production tubing.

The invention can of course be embodied in a variety of ways other thanas specifically described and illustrated.

I claim:
 1. A well completion system comprising:a plurality of downholecompletion assemblies, supply means carrying a fluid and an electricalsupply, said supply means comprising three concentric tubular electricalconductors, dielectric sleeves between said tubular conductors, andtubing concentric with said tubular conductors defining at least onefluid supply path, and means mounting said completion assemblies incommunication with said supply means.
 2. The well completion system ofclaim 1 wherein each of said downhole completion assemblies comprises afluid flow control means for controlling flow of fluid through saidassembly and operator means for selective adjustment of said flowcontrol means.
 3. A well completion system comprising:wellheadequipment, at least one downhole completion assembly, production tubingextending between said wellhead equipment and said at least onecompletion assembly, power tubing extending within said productiontubing between said wellhead equipment and said at least one completionassembly, said power tubing comprising at least one tubular electricalconductor, and at least one of a logging and a monitoring means carriedby said power tubing in operative association with said wellheadequipment by way of said tubular electrical conductor.
 4. The wellcompletion system of claim 3 further comprising a selectively adjustableflow control device for controlling flow of production fluid into saidproduction tubing to any selected one of a variety of substantial flowrates, and a control unit for controlling said control device, saidcontrol unit being carried by said power tubing.